The incident happened on Thursday 12 March at 10.30pm.
A man is reported to have exposed himself then began touching himself inappropriately – he left the train at Harrogate.
Officers would like to speak to the man in the image who may have information that could help their investigation.
Anyone who knows him is asked to contact BTP by texting 61016 or by calling 0800 40 50 40.
Quote reference number 642 of 12/03/20.
Alternatively, call Crimestoppers anonymously on 0800 555 111.